The overall goal of this project is to develop a novel mucosal vaccine for generating rapid and effective pulmonary immunity against aerosolized Yersinia pestis. These studies will focus on a novel vaccine delivery system that consists of liposome-antigen-nucleic acid complexes (LANAC). Our preliminary studies indicate that LANAC vaccines can elicit marked and long-lived T cell responses against both peptide and protein antigens, with an efficiency that in most cases exceeds that elicited by viral-vectored or dendritic cell vaccines. Moreover, preliminary data also indicate that LANAC vaccines can elicit marked intrapulmonary immunity and humoral immunity and are effective after mucosal administration. The ability to elicit strong cellular immunity may be particularly useful for control of Yersinia within infected macrophages. Therefore, the objectives of this proposal are to define the immunological mechanisms by which liposome-nucleic acid complexes enhance antigen presentation and to determine whether mucosal LANAC vaccines formulated with either Yersinia protein or peptide antigens can elicit protective immunity against aerosol challenge with Yersinia. The specific aims of this project are to (1) determine how liposomes and nucleic acids interact to enhance antigen presentation; (2) identify critical antigen-presenting cell targets for LANAC and how mucosal routes of immunization affect antigen presentation; (3) determine whether mucosal or parenteral vaccination with recombinant Yersinia F1 or V antigens can elicit protective immunity to aerosol challenge; (4) determine whether small secreted peptides from Yersinia can elicit protective CTL responses. These studies have relevance to the stated objectives of this RFA because they will yield important mechanistic information on a novel vaccine adjuvant for use in immunization against plague and other Category A-C agents. In addition, this project will provide critical proof-of-principal validation of the LANAC vaccine approach and the ability to elicit rapid pulmonary immunity against inhaled Yersinia, particularly after mucosal immunization.